The present invention relates to an exhaust gas-driven turbo-charger as claimed in claim 1. Such an exhaust gas-driven turbo-charger is known from the publication ""Kraftfahrtechnisches Taschenbuch/Bosch"" (Pocket book on motor vehicle technology), 21st edition, 1991, page 420 ff.
In exhaust gas-driven turbo-chargers for passenger car engines it is necessary to provide a control of the exhaust gas-driven turbo-charger in order to achieve a near constant boost pressure in the widest possible speed range as a result of the large speed range in passenger car engines. According to the prior art, a control on the exhaust gas side is known in which a portion of the exhaust gas from the engine is guided past the turbine (bypass). The control member required for this purpose can be arranged as a valve or flap. The required control pressure is tapped on the pressure side in the exhaust gas-driven turbo-charger, such that the system of the exhaust gas-driven turbo-charger with the boost pressure control member represents an independent unit.
An energetically more favourable control allows the variable turbine geometry, with which the back pressure behavior of the turbine is charged continuously and thus the entire exhaust gas energy can be used.
From the known embodiments, adjustable guide blades have become generally accepted due to their considerable control range with simultaneously favourable efficiency levels. As a result of the rotary movement of an adjusting ring it is possible to perform an adjustment of the blade angle in a very simple manner. The blades are set to the desired angle either by way of twist cams or directly by way of adjusting levers attached to the blades. Triggering occurs pneumatically by way of an adjusting dashpot with overpressure or underpressure. A microelectronic control can appropriately utilise the advantages of variable turbine geometry by optimal adaptation of the boost pressure over the entire motor diagram.
A variable turbine geometry (VTG), however, constitutes a considerable cost factor, so that in small engines with a smaller piston capacity turbo-chargers with VTG were unable to be generally established.
On the basis of the aforementioned, it is the object of the present invention to provide an exhaust gas-driven turbo-charger of the abovementioned type, which can be used at low cost for smaller engines with a controllable boost pressure.
This object is achieved according to the present invention by the features of claim 1.
The advantage of the invention is that in contrast to exhaust gas-driven turbo-chargers with variable turbine geometry no complex adjusting mechanisms are provided which control the direction and the speed of the exhaust gas flow prior to wheel approach, but that instead the adjustment of the turbine throughput is performed by way of a multi-fluted turbine housing, whereby a second afflux port can be switched on successively by means of the coupler. Impacting of the turbine with exhaust gas can accordingly be influenced by means of a simple, annular coupler directly through opening and closing of an afflux port.
A further advantage is that compared to exhaust gas-driven turbo-charger having variable turbine geometry, in which the highest efficiency is achieved only with approximately 50% of the maximum exhaust gas current, in the case of the exhaust gas-driven turbo-charger according to the present invention the highest efficiency occurs with minimal mass flow, that is, with minimal engine speed. This leads to improvement in the engine torque in the lower rpm range, which is particularly desirable in small-volume engines. This effect results in particular from the multi-fluted, preferably double-fluted, design of the exhaust gas-driven turbo-charger, such that when the coupler is closed the single-fluted impinging for low rpm ranges can be optimized and opened successively only with increasing engine speed of the coupler.
In a further embodiment the bypass port is opened beyond the open position with actuation of the coupler so that the boost pressure can be restricted. It is to be noted here that adjustment of the boost pressure ratio is enabled both by a rise in throughput by opening of another flute and by a drop in the mass current by opening the bypass, by means of only one servo component, the coupler.
Further advantageous embodiments of the invention will emerge from sub-claims 2 to 20.